Diagenetic Process and Their Effect on Reservoir Quality in Miocene Carbonate Reservoir, Offshore, Sarawak, Malaysia

Acta Geologica Sinica (Eng)

Alansari

2020

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Carbonate rocks are important hydrocarbon reservoirs around the globe and in Southeast Asia a key one, particularly, is the Central Luconia province. Understanding the internal characteristics, distribution, geometry and lateral extent of these rocks is essential for exploration and production success. Detailed work on Miocene carbonate reservoir facies, north of Bintulu, offshore Sarawak includes qualitative and quantitative analysis of photomicrographs and reservoir quality, considering especially microporosity. Stratigraphically, these carbonates are known as Cycles IV and V and are represented by eight major facies types (F-1 to F-8]. They comprise: coated grain packstone (F-1) (av. Ø = 3%, av. Kh = 0.5 mD) (av = Average; Ø = total porosity, and Kh = permeability); massive coral lime grainstone (F-2) (av. Ø = 14.7%, av. Kh = 6 mD); oncolite lime grain-dominated packstone (F-3) (av. Ø = 10%, av. Kh = 4 mD); skeletal lime/dolo-packstone (F-4) (av. Ø = 15%, av. Kh = 4.6 mD); coral (platy) lime mud-dominated packstone (F-5) (av. Ø = 4%, av. Kh = 0.5 mD); coral (branching) lime-dominated pack-grainstone (F-6) (av. Ø = 15%, av. Kh = 1 mD); cross-bedded skeletal lime packstone (F-7) (av. Ø = 20%, av. Kh = 2 mD); and bioturbated carbonate mudstone/chalk (F-8) (av. Ø = 8%, av. Kh = 0.8 mD). Study of thin sections reveals that red algae, foraminifera, and corals are the dominant fossil components with a minor admixture of skeletal fragments of echinoderms, bivalves, bryozoans, and green algae. All parameters, e.g., facies characterization, petrography, porosity-permeability value, and microporosity value were utilized to obtain a reliable reservoir quality. The microporosity value was quantified using digital image analysis software and is significant for recognition of good reservoir quality. Consideration of the presence of microporosity against the total porosity in the carbonate rocks has improved the correlation coefficient (R²) value, which has increased from 0.51 to 0.82.

Section: Petrophysical Properties and Reservoir Quality Based On Depomentioning

confidence: 67%

Offshore Carbonate Facies Characterization and Reservoir Quality of Miocene Rocks in the Southern Margin of South China Sea

Acta Geologica Sinica (Eng)

Alansari

2020

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“…Each cycle reflectsa different depositional environment, which is later modified by different diagenetic processes. Petrographic observation reveals that micritization, cementation, mechanical compaction, chemical compaction and dissolution are by far the most dominant diagenetic processes which have affected the reservoir quality ( Figure. 3) (Janjuhah et al, 2017b). The subaerial exposure during the regression is evident by the leaching of corals in F-2 and the skeletal debris in F-4.…”

Section: Facies Analysis and Petrographic Observationmentioning

confidence: 99%

Development of Carbonate Buildups and Reservoir Architecture of Miocene Carbonate Platforms, Central Luconia, Offshore Sarawak, Malaysia

SPE/IATMI Asia Pacific Oil &Amp; Gas Conference and Exhibition

Salim

Ali

et al. 2017

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Carbonate platforms in the Central Luconia is the most important province in the Sarawak Basin for gas production in the region. These carbonates are economically significant containing 65 trillion cubic feet of gas in place with minor contribution of oil rims. Over 200 carbonate buildups have been seismically mapped, out of which 120 still remain undrilled. These provide potentially attractive exploration targets and incentives to discover the remaining hydrocarbons in the region. The Central Luconia Province is a key geological unit for understanding the distribution of hydrocarbon resources in Malaysia. Although the first hydrocarbon was discovered more than 60 years ago,nevertheless, little effort has been made until now to address the proper facies scheme, cyclicity and reservoir quality of these Tertiary carbonates of Central Luconia. This paper documents the various facies based on the qualitative and quantitative description of cores of five wells cores in three different carbonate platforms with different cyclicity, carbonate buildups and reservoir quality. Detailed petrographic and petrophysical data have been validated to establish the standardized facies scheme. The combination of facies with cyclicity is very important to understand the depositional setting of the sediments and reservoir behavior. Because the sediments which are deposited during the transgressive phase can act as a barrier for hydrocarbon to migrate vertically. Eight facies types have been recognized qualitatively and quantitatively (Table-1), namely F-1 coated grain packstone, F-2 coral (massive) lime pack-grainstone, F-3 oncolite lime grain dominated packstone, F-4 skeletal lime/dolo packstone, F-5 coral (platy) lime mud dominated packstone, F-6 coral (branching) lime dominated pack-grainstone, F-7 cross bedded skeletal lime packstone, and F-8 bioturbated carbonate mud stone (chalk). These eight facies reflect different depositional environments ranging from lagoon to off reef settings. Overall, cores from the five wells consist of 80% of limestone, 15% of dolomitic limestone and 5% of dolomite and argillaceous limestone. The facies consist of eight dominant components comprising, 35%of coral, 30% of red and green algae, 30% of skeletal debris with 5% of other bioclasts. Moldic porosity is dominant (up to 45%), with the remaining are interparticle, intraparticle, vuggy and fracture porosity. 2 SPE-186979-MS Six regressive cycles are recognized within the carbonates based on the core and well logs. The 0.1 to 50m thick facies is stacked in vertical sequence within the 50-100m thick transgressive and regressive cycles. The reservoir intervals are divided into seven zones, based on porosity, permeability and major diagenetic events, representing high and tight porosity. The best reservoir intervals are consistently found in most of the regressive cycles, which composed of skeletal lime packstone, coarse coral fragments with touching vugs. The systematic semi-quantitative characterization, portrayed the buildup as coarse limestone with...

“…8). Four different diagenetic environments have been characterized, including marine phreatic, meteoric phreatic, minor mixing zone and burial (Longman, 1980;Vincent et al, 2007;Xi et al, 2015;Janjuhah et al, 2017b).…”

Section: Diagenetic Sequencementioning

confidence: 99%

“…These diagenetic processes signify specific alterations to conditions, which modified the sedimentary rock over time. The shallow diagenetic processes include micritization, cementation, compaction (physical and chemical), dissolution and dolomitization (Dixon et al, 1989;Scholle and Ulmer-Scholle, 2003;Janjuhah et al, 2017bJanjuhah et al, , 2019b. These diagenetic processes exhibit specific alteration conditions, which coincide with the changes that occurred with the passage of time.…”

Section: Diagenesismentioning

confidence: 99%

Biostratigraphy, Depositional and Diagenetic Processes in Carbonate Rocks from Southern Lebanon: Impact on Porosity and Permeability

Acta Geologica Sinica (Eng)

Sanjuan

Alqudah

et al. 2021

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Carbonate rocks are gaining more importance as natural building stones, karst aquifers, and hydrocarbon reservoirs in many parts of the world, including the giant fields of the Middle East (Burchette, 2012). According to Ehrenberg and Walderhaug (2015), more than 50% of all hydrocarbon reserves are hosted in carbonate rocks. Various physico-chemical and biological processes are associated with the formation and modification of carbonate rocks, leading to dramatic changes in their storage capacity, petrophysical, elastic and textural properties (